Force sensor

ABSTRACT

A force measuring apparatus includes a housing located with respect to an axis and having axially front and rear sections. A plunger is centered on the axis, supported by the housing for axial movement, and has axially front and rear spring supports. A load cell is fixed to the housing behind the rear spring support. A front spring structure is compressed between the front section of the housing and the front spring support of the plunger, urging the plunger rearward. A rear spring structure is compressed between the load cell and the rear spring support. The rear spring structure urges the plunger forward and applies against the load cell a force that is measurable by the load cell.

TECHNICAL FIELD

This application relates to force sensors.

BACKGROUND

A force sensor includes a housing and a plunger projecting from the housing. The sensor outputs an electrical signal that is a function of a force applied to the plunger relative to the housing.

SUMMARY

A force measuring apparatus includes a housing located with respect to an axis and having axially front and rear sections. A plunger is centered on the axis, supported by the housing for axial movement, and has axially front and rear spring supports. A load cell is fixed to the housing behind the rear spring support. A front spring structure is compressed between the front section of the housing and the front spring support of the plunger, urging the plunger rearward. A rear spring structure is compressed between the load cell and the rear spring support. The rear spring structure urges the plunger forward and applies against the load cell a force that is measurable by the load cell.

Preferably, the spring structures together bias the plunger into a neutral position. From the neutral position, an external rearward force applied to the plunger will move the plunger rearward and increase the measurable force, and an external forward force applied to the plunger will move the plunger forward and decrease the measurable force. An extension limiting structure limits forward movement of the plunger to prevent full compression of the front spring structure. A retraction limiting structure limits rearward movement of the plunger to prevent full compression of the rear spring structure. The housing encases the front and rear support structures of the plunger, and a front section of the plunger is located in front of the housing. Prongs are attached to the plunger and project radially outward from the plunger. A device has pockets that rotatably capture the prongs to couple the plunger to the device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view of a vacuum cleaner including a handle;

FIG. 2 is a breakaway view of an upper portion of the handle, including a force sensor;

FIG. 3 is an exploded view of the upper portion of the handle;

FIG. 4 is a sectional view of the upper portion of the handle, with a plunger of the sensor shown in a neutral position;

FIG. 5 is a view similar to FIG. 4, with the plunger shown in a retracted position; and

FIG. 6 is a view similar to FIG. 4, with the plunger shown in an extended position.

DESCRIPTION

The apparatus 1 shown in FIG. 1 has parts that are examples of the elements recited in the claims. The apparatus 1 thus includes examples of how a person of ordinary skill in the art can make and use the claimed invention. It is described here to meet the requirements of enablement and best mode without imposing limitations that are not recited in the claims.

The apparatus 1 is a vacuum cleaner. It includes a base 10, a handle 14 extending upward from the base 10, and a filter bag 20 suspended from the handle 14. The base 10 includes a housing 24 defining a nozzle 26. Front and rear wheels 30 and 32 are rotatably connected to the housing 24 to enable wheeling the base 10 over a floor 34. A fan 36 in the housing 24 drives a flow of air that carries dirt from the floor 34, through the nozzle 26, the fan 36 and a fill tube 38, into the filter bag 20.

To move the base 10 about the floor 34, a handgrip 40 of an upper section 42 of the handle 14 is grasped by hand. The handle 14 is pivoted backward as indicated by arrow 43. A forward or rearward force is manually applied to the handgrip 40, as indicated by arrow 45, to push the base 10 forward or pull the base 10 rearward. A force sensor 50 within the handgrip 40 outputs a signal indicative of the direction and magnitude of the force applied to the handle 14. An electrically powered drive assembly 54 in the base housing 24 receives the signal. The drive assembly 54 rotates the rear wheels 32 in a direction corresponding to the direction of the force applied to the handle 14, with a torque and speed that are positively related to the magnitude of the force. The drive assembly 54 thus uses electrical power to assist the user in propelling the base 10 over the floor 34.

The upper section 42 of the handle 14 is shown in FIGS. 2-3. It includes the handgrip 40 and a stem 64. The stem 64 is in the form of a metal bar extending along an axis 65. The handgrip 40 surrounds the stem 64 and is axially slidable along the stem 64.

The handgrip 40 comprises two side sections 66 and 68. Each side section 66 and 68 includes first and second tubular bosses 71 and 72. The first bosses 71 are aligned with each other, abut each other, and are secured together by a screw 75. The first bosses 71 thus together comprise a first prong 77 (FIG. 2) extending from one side 66 of the handgrip 40 to the other side 68 of the handgrip 40. Similarly, the second bosses 72 are aligned with each other, abut each other, and are secured together by a screw 75 extending through second bosses 72. The second bosses 72 thus comprise a second prong 78 extending from one side 66 of the handgrip 40 to the other side 68 of the handgrip 40.

As shown in FIG. 4, the first and second prongs 77 and 78 extend through corresponding first and second slots 81 and 82 in the stem 64. The first and second slots 81 and 82 are elongated in the axial direction and are sized with respect to the prongs 77 and 78 to enable axial movement of the prongs 77 and 78 relative to the stem 64 while preventing transverse movement of the prongs 77 and 78 relative to the stem 64. The prongs 77 and 78 and slots 81 and 82 together thus enable axial movement of the handgrip 40 relative to the stem 64 while preventing transverse movement of the handgrip 40. The range of axial movement is limited by abutment of the prongs 77 and 78 with axial ends 89 of the slots 81 and 82.

The sensor 50 includes a housing 90 centered on the axis 65, with axially front and rear sections 92 and 94, a top 96 and a bottom 98. Upper and lower tabs 102 and 104 extend respectively upward from the top 96 and downward from the bottom 98. The housing 90 is located in a central slot 106 in the stem 64 and is secured in place by screws 108 (FIG. 3) that fasten the tabs 102 and 104 to the stem 64.

The sensor housing 90 defines a chamber 110. A front channel 112 extends forward from the chamber 110 through the front section 92 of the housing 90. The front channel 112 is bounded by a cylindrical bearing surface 114 of the housing 90.

A plunger 120, centered on the axis 65, projects forward from the housing 90. The plunger 120 has a cylindrical side surface 124. An axially front section 130 of the plunger 120 is located in front of the housing 90 and has two annular grooves 132 extending circumferentially about the cylindrical side surface 124. An axially rear section 140 of the plunger 120 is located in the chamber 110 and includes a flange 142 extending radially outward from the cylindrical side surface 124. The flange 142 has front and rear spring support surfaces 144 and 146.

An axially middle section 150 of the plunger 120 includes a portion of the cylindrical side surface 124. The side surface 124 of the middle section 150 is diametrically the same size as, closely received by, and slidable relative to the bearing surface 114 of the housing 90. The bearing surface 114 enables axial movement of the plunger 120 while preventing radial movement of the plunger 120, to keep the plunger 120 centered on the axis 65. The plunger 120 is thus supported by the housing 90 for axial movement.

A load cell 160 is fixed to the rear section 94 of the housing 90. The load cell 160 is located in the chamber 110, rearward from the rear spring support surface 146 of the plunger 120. The load cell 160 outputs an electrical signal that is a function of a force applied to it.

A front spring structure 170 in the chamber 110 includes a front coil spring 172 and a metal washer 174. The coil spring 172 is compressed between the washer 174 and the front spring support surface 144 of the plunger 120. Accordingly, the front spring structure 170 is compressed between the front section 92 of the housing 90 and the front spring support surface 144 of the plunger 120. The front spring structure 170 thus urges the plunger 120 rearward. The front coil spring 172 is coiled about the plunger 120, which helps keep the spring 172 radially centered on the axis 65.

A rear spring structure 180 in the chamber 110 includes a rear coil spring 182 and a metal plug 184 that abuts the load cell 160. The rear coil spring 182 is compressed between the metal plug 184 and the rear support surface 146 of the plunger 120. Accordingly, the spring support structure 180 is compressed between the load cell 160 and the rear support surface 146 of the plunger 120. The rear spring structure 180 thus urges the plunger 120 forward and applies, against the load cell 160, a force that is measurable by the load cell 160. The spring structures 170 and 180 together bias the plunger 120 to an axially neutral position relative to the housing 90. The coil springs 172 and 182 and the plunger 120 are centered on the axis 65.

As shown in FIGS. 2-3, two C-clamps 190 are clipped into the two plunger grooves 132. Closely captured by and between the C-clamps 190 is a coupling bracket 200. The bracket 200 includes a rectangular plate 202 that closely receives the plunger 120. Two cylindrical prongs 204 and 206 project transversely outward from transversely opposite sides of the plate 202. The prongs 204 and 206 are thus attached by the plate 202 to the plunger 120 and project radially outward in diametrically opposite directions. The two prongs 204 and 206 are rotatably captured in respective pockets 214 and 216 in the respective handgrip sections 66 and 68. The bracket 200 thus couples the plunger 120 to the handgrip 40, for the plunger 120 to move in unison with the handgrip 40. Accordingly, the biasing of the plunger 120 toward its neutral position relative to the sensor housing 24 biases the handgrip 40 toward a neutral position relative to the handle stem 64.

In this example, the sensor housing 90 is connected to the handle stem 64, and the plunger 120 is connected to the handgrip 40. Alternatively, the sensor housing 90 can be connected to the handgrip 40, and the plunger 120 can be connected to the handle stem 64.

In FIG. 5, the plunger 120 is shown in a retracted position, displaced axially inward from its neutral position. The plunger 120 is retracted by applying a manual force 221 to the handgrip 40, against the bias of the sensor 50, toward the front of the vacuum cleaner 1 (FIG. 1). In turn, the handgrip 40 applies a force, which is external with respect to the sensor 50, to the plunger 120, pushing the plunger 120 axially inward against the bias of the rear spring structure 180. This increases the force that is applied by the rear spring structure 180 against the load cell 160 and measured by the load cell 160.

The retracted position of the plunger 120 in FIG. 5 is a fully retracted position in that further axially inward movement of the plunger 120 is prevented by abutment of the first handgrip prong 77 against an end surface 89 of the first slot 81. Accordingly, the first prong 77 and the end surface 89 comprise a retraction limiting structure that limits axially inward movement of the plunger 120. Axially inward movement is also prevented by abutment of one of the C-clamps 190 against the front 192 of the sensor housing 90. Accordingly, the C-clamp 190 and the front 192 of the housing 90 comprise another retraction limiting structure. The retraction limiting structures prevent full compression of the rear coil spring 182 and thus the rear spring structure 180. They also protect the load cell 160 from overload force by limiting the force the rear spring 182 can apply to the load cell 160. The retraction limiting structures are located outside the housing 90 in this example, but can be located in the housing 90.

In FIG. 6, the plunger 120 is shown in an extended position, displaced axially outward from its neutral position. The plunger 120 is extended by applying a manual force 231 to the handgrip 40, against the bias of the sensor 50, away from the front of the vacuum cleaner 1 (FIG. 1). In turn, the handgrip 40 applies a force, which is external with respect to the sensor 50, to the plunger 120, pulling the plunger 120 axially outward against the bias of the front spring structure 170. This decreases the force that is applied by the rear spring structure 180 against the load cell 160 and measured by the load cell 160.

The extended position of the plunger 120 in FIG. 6 is a fully extended position in that further axially outward movement of the plunger 120 is prevented by abutment of the first and second handgrip prongs 77 and 78 against end surfaces 89 of respective slots 81 and 82. Accordingly, the first prong 77 and an end surface 89 of the first slot 81 comprise a first extension limiting structure. Similarly, the second prong 78 and an end surface 89 of the second slot 82 comprise a second extension limiting structure. Each extension limiting structure limits axially outward movement of the plunger 120 to prevent full compression of the front coil spring 172 and the front spring structure 170. Even in the absence of the first and second extension limiting structures, full compression of the front coil spring 172 would be prevented by abutment of the plunger flange 142 against a shoulder 232 of the housing 90. Accordingly, the plunger flange 142 and the shoulder 232 comprise a third extension limiting structure, located in the housing 90.

A processor 240 in the housing 24 communicates with the load cell 160 to output the signal that is indicative of the force externally applied to the plunger 120. In this example, the signal is analog, with a range of 0-5V, and 2.5 volts being output when the plunger 120 is in its neutral position. The output voltage will increase in response to increasing force applied by the rear spring structure 180 against the load cell 160 due to increasing axially inward force externally applied to the plunger 120. Conversely, the output voltage will decrease in response to decreasing force applied by the rear spring structure 180 against the load cell 160 due to increasing axially outward force externally applied to the plunger 120. The drive assembly 54 (FIG. 1) receives the analog signal though wires 250 and drives the rear wheels 32 in a direction and with a force and speed based on the signal as explained above.

Alternatively, the signal that is output by the processor 240 to the drive assembly 54 can be digital. The range can be 0-255 counts, with 128 counts being output when the plunger 120 is in its neutral position. The counts will increase with increasing axially inward force externally applied to the plunger 120, and will decrease with increasing axially outward force externally applied to the plunger 120.

This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to make and use the invention. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims. 

1. A force measuring apparatus comprising: a housing located with respect to an axis and having axially front and rear sections; a plunger centered on the axis, supported by the housing for axial movement, and having axially front and rear spring supports; a load cell fixed to the housing behind the rear spring support; a front spring structure compressed between the front section of the housing and the front spring support of the plunger, urging the plunger rearward; and a rear spring structure compressed between the load cell and the rear spring support, urging the plunger forward and applying against the load cell a force that is measurable by the load cell.
 2. The apparatus of claim 1 wherein the spring structures together bias the plunger into a neutral position from which an external rearward force applied to the plunger will move the plunger rearward and increase the measurable force and an external forward force applied to the plunger will move the plunger forward and decrease the measurable force.
 3. The apparatus of claim 1 wherein the plunger has a radially outwardly extending flange with front and rear surfaces that respectively comprise the front and rear spring supports.
 4. The apparatus of claim 1 wherein the front spring structure includes a coil spring surrounding the plunger.
 5. The apparatus of claim 1 further comprising an extension limiting structure that limits forward movement of the plunger to prevent full compression of the front spring structure.
 6. The apparatus of claim 1 further comprising a retraction limiting structure that limits rearward movement of the plunger to prevent full compression of the rear spring structure.
 7. The apparatus of claim 1 wherein the housing encases the spring supports of the plunger.
 8. The apparatus of claim 1 wherein a front section of the plunger is located in front of the housing.
 9. The apparatus of claim 1 wherein the front section of the housing defines an axially extending channel that closely receives the plunger so as to enable axial movement of the plunger while preventing radial movement of the plunger.
 10. The apparatus of claim 1 further comprising prongs attached to the plunger and projecting radially outward from the plunger.
 11. The apparatus of claim 10 further comprising a device with pockets that rotatably capture the prongs to couple the plunger to the device.
 12. The apparatus of claim 10 further comprising a plate by which the prongs are attached to the plunger, that closely receives the plunger and from which the prongs project radially outward.
 13. The apparatus of claim 1 further comprising a vacuum cleaner handle including a handle stem and a handgrip slidably attached to the stem, one of the stem and the handgrip being fixed to the housing, and the other of the stem and the handgrip being fixed to the plunger, for the force measurable by the load cell to be indicative of a force manually applied to the handgrip relative to the stem.
 14. A force measuring apparatus comprising: a housing located with respect to an axis and having axially front and rear sections; a plunger centered on the axis, supported by the housing for axial movement, and having a spring support; a load cell fixed to the housing behind the rear spring support; a spring structure compressed between the load cell and the spring support of the plunger, urging the plunger forward and applying against the load cell a force that is measurable by the load cell; and a retraction limiting structure that limits rearward movement of the plunger to prevent full compression of the rear spring structure.
 15. The apparatus of claim 14 wherein the housing encases the spring support of the plunger. 